The present invention relates to a method of controlling the starting of a direct-injection internal combustion engine in which a supply fuel is delivered to said engine by means of pressurizing said fuel.
FIG. 1 of the appended drawing depicts a device for supplying a direct-injection internal combustion engine with fuel, the device being of a known type comprising a tank 1 of fuel, an electric pump 2 supplied by the tank 1 and associated with a pressure regulator 3 for delivering fuel to a second pump, through a filter 4, the fuel delivered by the pump 2 being raised to a first pressure level higher than atmospheric pressure, but still relatively low, hence the name xe2x80x9clow-pressure pumpxe2x80x9d given to the pump 2. The second pump 5, driven mechanically by the engine, raises the pressure of the fuel still further, to a second level, higher than the first, suitable for supplying fuel injectors 61, 62, 63, 64 mounted on an injection line 7 for supplying fuel to the cylinders of the direct-injection internal combustion engine (not depicted).
The pressure of the fuel delivered by the pump 5, known as the xe2x80x9chigh-pressure pumpxe2x80x9d, is fixed by an electromechanical regulator 8, such as an electrically operated valve controlled by a computer 9. In this last case, a sensor 10 delivers to the computer 9 a signal representative of the pressure P of the fuel contained in the line 7, so as to allow the computer to regulate the pressure of the fuel in this line to the required predetermined level which is of the order of 50 to 100 bar. The computer 9 commonly consists of the engine management computer, which, amongst other things, controls the injectors 6i (i ranging from 1 to 4 in the example depicted) and, in particular, the times for which they are open.
The fuel not delivered by the injectors 6i is returned to the tank by a pipe 11, 12 at atmospheric pressure.
According to a known method of starting a direct-injection internal combustion engine supplied by the device depicted in FIG. 1, this starting is performed with fuel delivered to the injectors 6i of the engine at a relatively low pressure (4 to 5 bar) achieved rapidly by the low-pressure pump which, being electrically operated, can be powered as soon as the vehicle (ignition) is switched on, before the engine is turned over.
In the case of a direct-injection internal combustion engine, however, starting at low fuel pressure entails resorting to an air/fuel mixture of a richness very much higher than that of a stoichiometric mixture, of the order of 10 times higher, the composition of this mixture at the spark plugs conventionally arranged in the cylinders of the engine to ignite it not being optimal in an engine of this type which is designed to be supplied in the normal way with fuel at high pressure, higher than 50 bar. This results in excessively long engine starting times, particularly in environments at low or very low temperature, and in a significant quantity of unburned hydrocarbons in the engine exhaust gases while the engine is starting.
The object of the present invention is precisely to provide a method of controlling the starting of a direct-injection internal combustion engine which does not have these disadvantages and which, in particular, makes it possible to shorten the engine starting time at low and very low temperatures, while at the same time then reducing the production of unburned hydrocarbons.
This object of the invention, together with others which will become apparent from reading the description which will follow, is achieved using a method of controlling the starting of a direct-injection internal combustion engine in which a supply fuel is delivered to said engine by means of pressurizing said fuel, this method being notable in that, during said starting, a) the temperature T of the engine and the pressure P of the fuel delivered by said pressurizing means are monitored, b) if T is below a predetermined threshold temperature Ts, an engine starting mode is established in which the engine is started with fuel at high pressure as soon as the pressure P becomes higher than a predetermined threshold pressure Ps1 and c) an engine starting mode is established where the engine is started using fuel at low pressure if T greater than Ts.
As will be seen later on, by normally starting the engine in this way, using fuel at high pressure rather than, as is conventional, at low pressure, the above-mentioned objectives are achieved.
According to another feature of the method according to the invention, in the starting mode using high-pressure fuel, if the fuel pressure remains higher than a predetermined threshold Ps2 which is lower than the threshold Ps1, a quantity of fuel to be injected into each cylinder of the engine is calculated and from this are deduced the length of time for which the injector considered is open and the time at which the injector opens, so as to allow said injection to close, in phase with an angular position of the engine crankshaft which is advanced by a predetermined angle with respect to the time that the air/fuel mixture is ignited.